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Canine transmissible venereal tumors, such as the one shown here, affect dogs of all breeds.
Claudio Murgia
Scientists have identified a common sexually transmitted canine tumor that can spread from dog to dog. Canine transmissible venereal tumor (CTVT) is probably the oldest cancer known and retains the same genetic structure it had when it began in a single wolf or dog there are more than 0 years. More broadly, the finding casts doubt on longstanding theory about the genetic instability in cancer cells and raises new questions about the evolution of the tumor.
CTVT is a common, usually not lethal, a cancer that affects dogs of all races worldwide. Scientists thought once it was caused by a transmissible virus, much like cervical cancer in humans, but recent studies have suggested the tumor cells themselves are spread from dog to dog, perhaps be during intercourse or oral contact with tumors.
Probing this theory, virologists led by the University College London scientist Robin Weiss took samples of tumor and blood from 16 dogs from three countries. DNA analysis revealed strong genetic similarities between tumors, evidence that tumor cells came from a common ancestral cell. In addition, there were no genetic correspondence between tumors and dogs, that would be expected if the tumors were raised by transferring clean a dog cells. After examining the genetic structures of tumors taken from 24 other dogs from five other countries, the team determined that the cancer must be from an animal, probably a wolf or an old gray dog breed there are between 0 and 2500 years.
scientists suspect that CTVT arose first in one inbred herding dogs or wolves, which would have made the immune system more responsive dogs foreign tissue. Shortly after it has developed, said Weiss, cancer divided into two sub-populations, both of which are found in dogs today. The most likely cancer was more virulent in the beginning, but Weiss said, it seems to have evolved to allow the canine immune system to defeat - but not before the disease is transmitted to another dog. The work appears in August 11 issue of Cell
The conclusion -. A line of cancer cells in existence for over 0 years - challenges the notion that cancer cells become more aggressive as they evolve, eventually becoming genetically unstable and more vulnerable to drugs and the body's immune system, said Weiss. "I think this tumor tells us to think more broadly about the stability of the genome and genomic instability in cancer."
There have been no documented cases of human transmissible cancers; however, there was one case of animal. Last year, scientists in Australia released research suggesting that cancer of the face that decimated the wild Tasmanian devil population is transmissible ( Science , 18 February 05). There is no relationship between tumors, but there is a common concern for conservation biologists, said Elaine Ostrander with the American Institute National Human Genome Research in Bethesda, Maryland. "The idea that infectious tumors there is a new concern for threatened or endangered species," she said. "It would not surprise me if there are more cases of this kind that come along."
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